My invention is in the field of collision preventing for trains. My intention is to control the trains automaticly to follow the traffic lights, so collisions can be prevented. Briefly, the inventions in this field can be grouped into four categories. First category includes those inventions employing high frequency signals transmitted from the wayside to the locomotive to express red, yellow and green traffic lights. The second category includes those inventions using the two track rails as communication cables between two trains. The third category includes those inventions applying high frequency space signals to communicate between two trains or between trains and stations. The fourth category includes those inventions employing D. C. voltages transmitted from the wayside to the locomotive.
The first invention in the first category found in the U.S. patent publications was by Bushnell. He employed two inductances, one placed on the wayside and one placed on the locomotive, the signals can be transmitted from the wayside to the locomotive by interinduction between the two inductances. This invention was improved later by himself, Peter et al., Freeman, Horeezky and others. The main disadvantage of those inventions in this category is that the high frequency space signals transmitted from the wayside to the locomotive, may be easily interfered with by other space signals. The interference may cause the frequency of the signals transmitted to the locomotive to shift. Such frequency shift may result in a wrong expression of the traffic lights. The frequency expressing a red traffic light may be shifted to the frequency expressing yellow or green traffic light. This may cause the train to run on a red traffic light and to collide with another train on the way. A typical example in the second category was the invention of Carrino, Lardennois et al.. One requirement in their invention was to insulate electrically the axles from the wheels, so the two track rails will not have a short circuit caused by the axles. This kind of insulation is almost impossible, besides, the axles should not be insulated from the wheels so, the axles plus the two rails can become a part of a circuit for other purposes. An example in the third category was the invention of Helmoke et al., Schonbrodt and Listing. They invented some device similar to radio transmitters and receivers to be installed on the locomotive, which could measure the distance of approaching trains. This kind of device will be very costly and also will have the problem of interference. Also, the distance measured by the device will not be accurate when the rail way truck curves. Finally, there are two examples in the fourth category. They are the inventions of Wyant and Rosenthal. They invented devices to transmit a D. C. voltage of positive or zero value from the wayside to the locomotive. My invention can be classified into the fourth category. I employ D. C. voltages of zero, positive and negative values to represent red, yellow and green traffic lights.